(1) Field of the Invention
The present invention lies in the technical field of buoyancy systems enabling an aircraft to ditch on water. The present invention relates to a method of automatically triggering an emergency buoyancy system for an aircraft and in particular for a hybrid helicopter. The present invention also relates to an emergency buoyancy system that implements the method, and to a hybrid helicopter including such a system.
(2) Description of Related Art
An emergency buoyancy system contributes to enabling an aircraft such as a helicopter to float in stable manner in the event of ditching on water, in particular so as to enable the occupants of the aircraft to evacuate it. Aircraft used for missions involving transporting people over the sea are in principle fitted with such an emergency buoyancy system.
Aviation operating regulations require in particular that helicopters used for transporting passengers and overflying large stretches of water to demonstrate their ability to ditch on water. Ditching is the helicopter making contact with the surface of the water while also keeping the helicopter balanced on the surface of the water. This balance must be ensured while the main rotor of the helicopter is still rotating, and throughout the entire transient stage of stopping the main rotor, and finally after the main rotor has stopped.
As a general rule, an emergency buoyancy system comprises a plurality of floats situated in the bottom portion of the aircraft fuselage. These floats are generally inflatable bags that are inflated by one or more fluid generators, which generators may be tanks of gas under pressure or they may be of the pyrotechnic type, for example.
On present aircraft, inflation of the floats may be controlled manually by the pilot or the copilot of the aircraft, or it may be triggered automatically as a result of one or more immersion sensors detecting that the aircraft is ditching by coming into contact with water. Nevertheless, the buoyancy system must initially be primed using a dedicated control button, where priming is performed when overflying the sea. The purpose of priming the buoyancy system is to limit any risk of untimely triggering.
For aircraft having rotating elements, it is preferable to ensure that the rotating elements do not come into contact with the surface of the water when ditching. If they come into contact with the surface of the water, there is a risk of some or all of these rotating elements breaking up and being projected, which can then give rise to major damage to the aircraft and to its emergency buoyancy system, and above all can lead to severe injury of the occupants of the aircraft.
With a conventional helicopter, a main rotor for providing lift or even propulsion is located sufficiently high relative to the aircraft, generally being above the fuselage, to minimize any risk of interference between the main rotor and the surface of the water.
In contrast, a hybrid helicopter has at least one rotating element for performing the propulsion and anti-torque function, such as a propulsive propeller, which element is in a position that makes it possible for it to come into contact with the surface of the water on ditching. For example, a hybrid helicopter may have two half-wings on either side of the fuselage, with each half-wing supporting a respective propulsive propeller.
Document FR 1 368 083 describes a helicopter having a single main rotor and a safety device to enable that helicopter to float on water. Such a safety device comprises a float that is permanently inflated and that is situated in the tail of the helicopter, together with two floats that are not inflated and that are positioned in the hubs of two landing gear wheels. That device also has two immersion sensors for triggering inflation of the floats by means of a gas generator.
Document FR 2 967 972 is also known, which describes a method of controlling an emergency buoyancy system for limiting the risk of untimely triggering. Such a buoyancy system has at least one float and means for inflating the float, together with priming means for activating the means for inflating the float, such that a float inflation order can subsequently be given manually, e.g. by the pilot, or else automatically by at least two immersion sensors.
In that method, the pilot or the copilot has a predetermined length of time to confirm or override an inflation order, thereby avoiding untimely inflation of each float. Nevertheless, certain conditions that correspond to a high probability of ditching lead to each of the floats being inflated immediately without waiting for pilot confirmation.
Also known is document FR 666 671,which describes an airplane having two wings, a central float, and two lateral floats positioned under the ends of each wing, thereby transforming that airplane into a hydroplane. That airplane also has landing gear under the central float that is provided with an axle having two wheels that also has a tail skid. The axle may be raised or lowered, thereby enabling the airplane respectively to alight on a water surface or else to land on a runway.
Furthermore, document FR 1 100 863 describes an airplane having a takeoff and landing system provided with a main single-track undercarriage, additional wing-tip undercarriages, and an auxiliary device that remains on the ground. The additional undercarriages are positioned under the wings and each of them has a retractable skid. The single-track main undercarriage has a steerable and retractable front wheel and a central skid that is also retractable. The auxiliary device is constituted by an axle and twin wheels that are positioned under the central skid during takeoff and that remain on the ground after takeoff. When landing, the airplane lands directly on the front wheels, the central skid, and the additional undercarriages.
Also known is the Sea Harrier® airplane that has additional undercarriages under each of its wings, also referred to as “outriggers”, suitable for stabilizing the airplane, but only on the ground.
Document GB 895 590 describes a helicopter having a main rotor, two half-wings, and two propulsive propellers mounted on respective half-wings and driven in rotation by respective independent and dedicated turbines. Each half-wing is downwardly foldable at its end, beyond the propulsive propeller. In addition, a fuel tank is positioned at the end of each half-wing and can act as a float when the ends of the half-wings are folded down, the helicopter then being on a water surface.
According to document U.S. Pat. No. 5,765,778,an aircraft has an emergency device made up of a plurality of auxiliary engines and inflatable balloons. The auxiliary engines are steerable and can act in particular to exert vertical thrust so as to reduce the rate of descent of the aircraft in the event of an emergency landing. The inflatable balloons are positioned in a bottom zone of the fuselage of the aircraft and they can be inflated instantly in order to damp the impact of such an emergency landing. The auxiliary engines also include protection enabling them also to damp the impact with the ground in the event of said emergency landing.
Finally, document WO 2012/113038 describes a buoyancy system having at least one inflatable bag, an inflation device, and a detection and activation system. The buoyancy system thus makes it possible to increase the buoyancy of the aircraft, in particular so as to have sufficient time available to enable the occupants of the aircraft to evacuate it in the event of ditching on water.